An aircraft gas turbine engine thrust reverser (T/R) functions to slow the forward speed of an aircraft either upon landing or during an aborted takeoff. The thrust reverser lessens wear to the landing gear brakes and allows for shorter runway length.
A translating sleeve style T/R features a sleeve structure that radially encapsulates a series of airflow vanes, commonly known as a cascade array, radially inward and outward with respect to the engine centerline. The trailing edge of the T/R on traditional embodiments forms the outer surface of the annular fan duct nozzle.
When the T/R is stowed the inner translating sleeve surface forms the outer wall of the engine fan duct and the outer surface forms part of the outer nacelle airflow surface.
When the T/R is deployed the sleeve structure translates aft while deploying blocking features into the fan duct. The blocking features, usually petal-style hinged panels, drop into the fan duct and force fan air radially through the cascade array which turns the flow outward and partially into the direction of aircraft travel thereby slowing forward motion.
A T/R generally comprises two semi-circular half segments, left and right, that operate in unison to generate reverse thrust.
On traditional engine designs the fan nozzle is fixed and generally designed to supply optimal efficiency at cruise speed and altitude. This creates engine noise and engine inefficiency during high thrust and low altitude operations.
In today's economic climate, fuel efficiency is of paramount importance and a need exists to customize an aircraft engine fan nozzle for all operational environments. Also, low aircraft noise is desirable as airline operations move away from large commercial hubs to smaller regional airports adjacent to population centers. Finally, dynamic pressures within the fan duct at high engine power can present a design challenge for aircraft engine designers. A Variable Area Fan Nozzle (VAFN) remedies these issues.
Current VAFN designs for practical use with translating sleeve thrust reversers introduce a new moving structure disposed on the trailing edge of the T/R that translates forward and aft in relation to the fan duct conical inner surface creating a variance in exit area. This structure can either be infinitely positionable between its two extremes or have discrete positions depending on functional requirements. As with the T/R, two semicircular VAFN half segments, left and right, operate in unison to create the complete fan duct exhaust nozzle.
As a translating VAFN forms the engine fan nozzle exit it must be located aft of the T/R translating sleeve. Also, in order to avoid interference when the T/R deploys the VAFN must also have a capability to move either in unison with or out of the way of the T/R translating sleeve for a plurality of positions between close and open.
Prior art VAFN designs have located actuation components on the T/R translating sleeve as disclosed in U.S Publication No. 2010/0229528 Ramlaoui et al. incorporated herein by reference in this specification. The sleeve is generally a relatively soft structure which slides on loose tracks and thus presents a high vibration environment. These designs also require many degrees of freedom in order to prevent binding of the actuator which is attached to the fixed engine structure, translating sleeve and VAFN. This adds unnecessary complexity and weight while reducing reliability and maintainability.
These prior art designs have only been able to sense nozzle position across the full VAFN stroke by using a dedicated position sensing system connected between the nozzle and the fixed structure where the control system is located, thus incurring a high weight penalty.
Thus prior art actuators, such as in Ramlaoui et al., have used multiple components in order to transmit motive force developed on the fixed T/R structure to the T/R translating sleeve and finally to the VAFN. This increases weight and makes for poor maintainability and higher complexity resulting in lower reliability.
Due to the layout of those actuation designs, large components can be located at the back of the driveline forcing the need for exaggerated aerodynamic fairings to house the actuation system. This increases both weight and aircraft drag.
Other VAFN embodiments of the prior art feature a plurality of sliding trackways disposed radially on a conic surface as disclosed in U.S. Pat. No. 8,127,531 Parham. This arrangement creates a bind rather than a free functioning system as the guides disposed circumferentially on the conic surface are not parallel to one another.
There have been attempts to integrate the VAFN and thrust reverser actuators into one unit as taught in French Patent Publication No. 2,922,059 Vauchel et al., and US Publication No. 2012/0137654 Burgess among others. This requires redundancy in components to isolate one system from the other in order to prevent a common mode, dual system failure. This yields no weight savings compared to separate actuation systems. Separate VAFN and T/R actuators allow for aircraft dispatch with one system failed while retaining the function of the other. This reduces maintenance time and cost because actuator replacement only requires one system to be repaired while the other remains unaffected. Also, this approach requires transmission of power from the fixed part of the T/R structure to the translating sleeve, then to the VAFN which requires more degrees of freedom resulting in increased weight.
Previous designs have attempted to pivot the entire thrust reverser translating sleeve in order to vary exit area as disclosed in U.S. Pat. No. 8,127,532 Howe incorporated herein by reference in this specification. This results in a significant weight penalty by introducing an intermediate pivoting structure between the thrust reverser translating sleeve and fixed nacelle structure.
The instant invention results for efforts to address one or more of the above identified problems.